CN113851664B - Method for preparing hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne, prepared material and application - Google Patents

Method for preparing hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne, prepared material and application Download PDF

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CN113851664B
CN113851664B CN202111263121.1A CN202111263121A CN113851664B CN 113851664 B CN113851664 B CN 113851664B CN 202111263121 A CN202111263121 A CN 202111263121A CN 113851664 B CN113851664 B CN 113851664B
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gdy
graphite alkyne
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CN113851664A (en
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蔡称心
潘永慧
周家兴
胡耀娟
乔玲
樊晶晶
吴萍
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Nanjing Normal University
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Abstract

The invention discloses a method for preparing an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst, a prepared material and application,the sp-N doped graphite alkyne nano hollow sphere electrocatalyst is SiO modified by polydiallyl dimethyl ammonium chloride 2 Ball as hard template, in SiO 2 Uniformly wrapping nitrogen-doped graphite alkyne on the surface of the ball, and finally removing SiO 2 The balls are formed. The electrocatalyst prepared by the invention has the advantages of coexistence of mesopores and micropores and high surface area, and is beneficial to the exposure of active sites and the improvement of mass transfer performance. The preparation flow of the sp-N doped graphite alkyne nano hollow sphere electrocatalyst is simple and easy to implement, the time is short, and compared with a commercial Pt/C catalyst, the catalyst has the electrocatalytic activity of the commercial Pt/C catalyst on oxygen reduction reaction under acidic or alkaline conditions, and meanwhile, the cost is lower, so that the catalyst is suitable for industrial production and can effectively promote the commercial development of fuel cells.

Description

Method for preparing hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne, prepared material and application
Technical Field
The invention belongs to the field of fuel cell electrocatalysis, and in particular relates to a method for preparing an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst, and a prepared material and application thereof.
Background
The design and development of energy conversion devices that are green, efficient and capable of large-scale commercialization is an important strategy to solve the environmental pollution and energy starvation problems faced by current humans. The fuel cell is a novel cell device, and compared with the production of traditional energy sources, the fuel cell can generate electricity by using chemical energy in fuel in a green and efficient way, and is not limited by the Carnot cycle effect in the reaction process. However, the slow kinetics of the Oxygen Reduction Reaction (ORR) severely limits its commercial development. Up to now, platinum (Pt) -based noble metal materials are the most effective electrocatalysts for promoting ORR processes, but Pt-based catalysts still cannot meet the requirements of large-scale applications due to their high cost, low methanol tolerance, poor electrochemical stability, and other drawbacks. Therefore, the exploration of a cheap, efficient and durable nonmetallic ORR electrocatalyst is of great importance for the development of green energy technology.
Heteroatom-doped carbon materials, particularly nitrogen-doped carbon materials (e.g., N-doped graphene), are of great interest in the field of oxygen reduction due to their controllable electronic properties, low cost, and good stability. Graphite alkyne (GDY) has been widely used in the energy field since it was successfully synthesized in 2010 as a new member of the carbon material family. Unlike other allotropes of carbon, GDY has a molecular structure consisting of sp and sp 2 The hybridized two carbon atoms, the existence of the two carbon atoms and the grid structure endow GDY with good chemical stability and special electronic structure and two-dimensional structure, so that the catalyst can be used as a good ORR catalyst substrate to improve the performance of the catalyst.
At present, related reports prove that the nitrogen doped graphite alkyne catalyst is a catalyst with good ORR, but GDY is easy to generate agglomeration and accumulation when being taken as a carrier, so that the specific surface area is greatly reduced, the mass transfer performance is poor, the oxygen transmission in the reaction process is not facilitated, and the active site covered by an agglomeration layer is difficult to contact with electrolyte and participate in electrode reaction, so that the further improvement of the catalytic activity is limited. The two-dimensional GDY structure is regulated to have a stable morphology (such as hollow spheres and nanotubes) with high specific surface area and porous structure, so that the problems can be effectively avoided. At present, the research on GDY morphology regulation is less, the preparation method is limited, and literature data (J.Phys.chem.C., 2011,115,2611-2615) reports a method for adding an AAO template to a precursor for synthesizing GDY to prepare a graphite alkyne nanotube, but the preparation method is complex, takes time (7 days for reaction), and has unstable structure. Therefore, further development of graphite alkynyl catalyst with simple preparation, low cost, high specific surface area and porous structure is of great significance for further improving the catalytic activity of ORR and the commercialization development of fuel cells.
Disclosure of Invention
The invention aims to: aiming at the problems existing in the prior art, the invention provides the hollow sphere electrocatalyst containing the sp-nitrogen doped graphite alkyne, which has a porous structure, a high specific surface area and a large number of active sites due to the unique morphology of hollow spheres and the existence of sp-N, shows excellent ORR catalytic performance and electrochemical stability in both acidic and alkaline environments, and can be effectively used for fuel cells.
The invention also provides a preparation method and application of the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne.
The technical scheme is as follows: in order to achieve the aim, the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne is SiO modified by polydiallyl dimethyl ammonium chloride 2 Ball as hard template, in SiO 2 Uniformly wrapping nitrogen-doped graphite alkyne on the surface of the ball, and finally removing SiO 2 The balls are formed.
In particular, the polydiallyl dimethyl ammonium chloride modified SiO 2 The ball is used as a hard template, and the small-sized graphite alkyne is uniformly coated on the SiO under the electrostatic action 2 Adding nitrogen-containing organic micromolecules as a nitrogen source on the surface of the ball, doping nitrogen elements into graphite alkyne through high-temperature pyrolysis treatment, and finally removing SiO 2 The ball is prepared.
Wherein, the internal diameter of the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne is the same as the size of the SiO2 sphere, and the thickness of the hollow sphere is 5-11nm. SiO in the present invention 2 Is used as a hard template, and graphite alkyne is uniformly coated on SiO 2 The thickness of the graphite alkyne is 5-11nm.
The preparation method of the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne comprises the following steps:
(1)SiO 2 modification of the ball: siO is made of 2 Adding the balls into NaCl solution for ultrasonic dispersion, then adding polydiallyl dimethyl ammonium chloride for stirring, centrifugally washing and vacuum drying to obtain modified positively charged SiO 2 A ball;
(2) Miniaturization of GDY: sufficiently grinding graphite alkyne, dispersing in water, and carrying out ultrasonic treatment to obtain a lamellar GDY solution with small size;
(3)SiO 2 preparation of @ N-GDY: the modified positively charged SiO obtained in the step (1) is subjected to 2 Dispersing the spheres in water, mixing and stirring the dispersion liquid with the small-sized lamellar GDY dispersion liquid obtained in the step (2), and centrifugally drying to obtain black solid SiO 2 @ GDY. SiO is made of 2 Grinding the @ GDY solid and the N-containing organic micromolecules, and carbonizing the ground N-containing organic micromolecules at high temperature in inert gas to obtain SiO 2 @N-GDY；
(4) Preparation of sp-N doped graphite alkyne nano hollow sphere electrocatalyst: siO obtained in the step (3) is reacted with 2 Dispersing @ N-GDY in an HF solution, stirring for etching, centrifugally washing the etched mixture to be neutral by deionized water, and vacuum drying to obtain the sp-N doped graphite alkyne nano hollow sphere electrocatalyst.
Wherein SiO in the step (1) 2 The mass ratio of the poly (diallyl dimethyl) ammonium chloride to the poly (diallyl dimethyl) ammonium chloride is 1-2:4.
wherein, the ultrasonic time in the step (2) is 1.5-3h, the ultrasonic power is 100-200W, and the concentration of the GDY liquid is 1-5mg/mL. The preferred concentration of GDY solution is 3mg/mL.
Preferably, in order to ensure GDY miniaturization, the ultrasonic power is 200W, and the ultrasonic time is 3h.
Wherein, in the step (3), siO with positive charge after modification is arranged 2 The ratio of the ball to the graphite alkyne is 1:0.25-1.
Wherein in the step (3), the N-containing organic micromolecule is any one of melamine, biuret and dicyandiamide, and SiO 2 The mass ratio of the @ GDY to the N-containing small organic molecules is 1:5-10.
Wherein, the inert gas in the step (3) is nitrogen or argon, the heating rate of high-temperature carbonization treatment is 5-10 ℃/min, the carbonization temperature is 700-900 ℃ and the carbonization time is 1-1.5h.
Wherein the volume concentration of the HF solution in the step (4) is 5-15%, and the etching time is 6-12h at normal temperature.
Preferably, the concentration of HF is 7-12%, the etching time is 5-8h, and the hollow sphere morphology is prevented from being strict due to too high concentration of HF or too long etching timeHeavy damage, too low HF concentration or insufficient etching time, resulting in SiO 2 There is a residue.
The invention relates to an application of an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst in a fuel cell cathode oxygen reduction reaction.
According to the invention, a template is used as a support, flaky graphite alkyne is converted into graphite alkyne hollow nanospheres with high specific surface area and porosity by a template method, and in the process of pyrolysis at high temperature, N-containing organic molecules and ethynyl in the graphite alkyne undergo a cyclic reaction, so that nitrogen atoms are uniformly doped in the graphite alkyne hollow nanospheres in an sp hybridization mode. The nitrogen doped graphite alkyne nano hollow sphere electrocatalyst is 0.5mol/L H due to the unique hollow sphere morphology and sp-N existence 2 SO 4 The solution (pH=0) and the 0.1mol/L KOH solution (pH=13) show excellent ORR catalytic performance, and the preparation scheme is simple and controllable and convenient for production.
When GDY is used as a carrier, agglomeration and accumulation are easy to occur, the specific surface area is greatly reduced, the mass transfer performance is poor, and the active sites covered by the agglomeration layer are difficult to contact with electrolyte and participate in electrode reaction, so that the two-dimensional GDY structure is regulated to have a stable morphology with a high specific surface area and a porous structure, and the problems can be effectively avoided. The existing preparation method is to add a template into a precursor synthesized GDY, so that the GDY can be successfully grown on the surface of the template, the synthesis time is seven days and the subsequent treatment is needed, the time consumption is long, the preparation process is difficult to control, the morphology is unstable, and the mass production is difficult. The method comprises preparing GDY (SiO is not added into GDY precursor) 2 ) GDY is then wrapped in SiO 2 Applying; the differences are: GDY takes about 2.5 days for synthesis, and the final catalyst prepared by the morphology modification method provided by the invention only takes 1-2 days; the original method directly adds a template to synthesize a precursor of GDY to regulate morphology, which takes 7 days. Therefore, the method provided by the invention is simpler and more convenient and saves time.
Based on the method, the innovation of the invention is to provide a simple and efficient method for synthesizing the morphology of the GDY hollow sphere and an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst. The method is simple to GDYThe two-dimensional structure of the material can be converted into the shape of the GDY hollow sphere by treatment, the operation is simpler, and the preparation period is greatly shortened. As shown in FIG. 1, siO is deposited 2 The ball is used as a hard template, and the small-sized graphite alkyne is uniformly coated on the SiO under the electrostatic action 2 Adding nitrogen-containing organic micromolecules as a nitrogen source on the surface of the ball, doping nitrogen elements into graphite alkyne through high-temperature pyrolysis treatment, and finally removing SiO 2 The N-GDYHS can be obtained by the ball. The sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst prepared by the invention has stronger electronegativity than C due to the doped sp-N, and after the catalyst is introduced into a graphite alkyne hollow sphere carbon carrier, electrons around the C can be transferred to the sp-N, so that the oxygen adsorption capacity of the C is improved. In addition, the construction of the hollow sphere morphology provides a larger specific surface area and a porous structure, so that reactants, catalytic active sites and electrolyte solution can be fully contacted, interface compatibility can be improved, better infiltration of the electrolyte solution is facilitated, overpotential is reduced, and the cycling stability of the material is further improved. Compared with an sp-N doped non-hollow structure graphite alkyne electrocatalyst (N-GDY) and an sp-N undoped graphite alkyne nano hollow sphere electrocatalyst (GDYHS), the sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst prepared by the invention has higher electrocatalytic activity and electrochemical stability under alkaline and acidic environments, and even can be comparable to the electrocatalytic activity of a commercial Pt/C catalyst, but the price of the N-GDYHS electrocatalyst prepared by the invention is significantly lower than that of the commercial Pt/C catalyst.
The invention focuses on converting the two-dimensional GDY into a hollow sphere structure, in particular to wrapping the miniaturized GDY on the modified SiO 2 The surface and the silicon dioxide ball are completely etched by HF, so that the problems that the two-dimensional GDY is used as a carbon carrier, agglomeration and accumulation are easy to occur, the specific surface area is greatly reduced, the mass transfer performance is poor, and an active site covered by an agglomeration layer is difficult to contact with electrolyte and participate in electrode reaction are solved. The hollow sphere structure has the advantages of providing a larger specific surface area and a porous structure compared with two-dimensional GDY, enabling sufficient contact between reactants, catalytic active sites and electrolyte solution, improving interfacial compatibility, facilitating electricityBetter infiltration of the solution, reduction of overpotential and further improvement of the circulation stability of the material. The method disclosed by the invention has the characteristics of short preparation period, simplicity in operation and controllable process.
The beneficial effects are that: compared with the prior art, the invention has the following advantages:
1. the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne prepared by the method has a porous structure, can effectively improve the specific surface area of GDY, is beneficial to promoting the full contact among reactants, catalytic active sites and electrolyte solution, is beneficial to improving interface compatibility, promotes better infiltration of electrolyte, reduces overpotential and further improves the stability of materials.
2. The sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst prepared by the invention has the initial potential and half-wave potential of a Pt/C catalyst and excellent electrochemical stability in oxygen reduction reaction tests under acidic and alkaline conditions, and has wide application prospect.
3. According to the invention, a template method is adopted, spherical silicon dioxide is used as a template, untreated flaky graphite alkyne is miniaturized and adsorbed on the surface of the template, and after high-temperature treatment and HF etching, the graphite alkyne nano hollow sphere structure with high specific surface area and porosity can be obtained. The conversion of the lamellar structure of the graphite alkyne into hollow spheres helps to increase the exposure of the active site and promote mass transfer processes during ORR.
4. The preparation process of the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne is simple and easy to implement. Compared with a commercial Pt/C catalyst, the electrocatalyst has lower cost, is suitable for industrial production, and can effectively promote the commercial development of fuel cells.
Drawings
FIG. 1 is a schematic diagram of the synthesis of an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst;
in FIG. 2a, b are SiO before and after modification, respectively 2 A transmission electron microscope image;
in FIG. 3a, b, c are GDY and GDY SiO-coated before and after sonication, respectively 2 Is a transmission electron microscope image;
in FIG. 4a, b are SiO after pyrolysis at high temperature, respectively 2 Transmissive electron microscope image of @ N-GDY and post-etch N-GDYHS;
FIG. 5 is a high resolution XPS spectrum of N1s in the sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst prepared in example 2;
FIG. 6 is a graph of a transmission electrode of a graphite alkyne hollow sphere electrocatalyst prepared in comparative example 1;
FIG. 7 is XPS total spectrum of the sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst prepared in example 2 and the graphite alkyne hollow sphere electrocatalyst prepared in comparative example 2;
FIG. 8 is a nitrogen adsorption/desorption isotherm of the sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst prepared in example 2 and the nitrogen doped graphite alkyne electrocatalyst prepared in comparative example 3;
FIG. 9 is a graph of linear sweep voltammetric measurements under alkaline conditions for example 2, comparative example 1, comparative example 2, comparative example 3, and commercial 20wt% Pt/C catalyst;
FIG. 10 is a graph of linear sweep voltammetric measurements under acidic conditions for the catalysts prepared in example 2, comparative example 1, comparative example 2, comparative example 3, and commercial 20wt% Pt/C catalysts;
FIG. 11 a is a graph of the timing amp curve of the catalyst prepared in example 2 and Pt/C in 0.1mol/L KOH solution; b is N-GDYHS and Pt/C is 0.5mol/L H 2 SO 4 A chronoamperometric curve in the solution;
FIG. 12 a is a transmission electron micrograph of the catalyst prepared in example 2 after long-term stability test in 0.1mol/L KOH solution; b is 0.5mol/L H for example 2 preparation of catalyst 2 SO 4 Transmission electron microscopy after long term stability testing in solution.
Detailed Description
The invention is further illustrated by the following examples.
The experimental methods described in the examples, unless otherwise specified, are all conventional; the reagents and materials, unless otherwise specified, are commercially available.
In the embodiment of the invention, the hard template SiO 2 Is by classical means
Figure BDA0003326268900000052
Prepared by the method (reference: J.colloid Interface Sci.,1968,26,62-69.) with an average diameter of about 280nm; GDY is synthesized by the method described in the reference (chem. Commun.,2010,46,3256-3258).
Example 1
By classical means
Figure BDA0003326268900000051
The method prepares SiO with the diameter of about 280nm 2 The ball acts as a hard template. 50mg of SiO to be prepared 2 Adding 0.5mol/L NaCl solution, performing ultrasonic dispersion for 1h, adding 0.2g polydiallyl dimethyl ammonium chloride (molecular weight 10,000 ～ 20,000) and stirring for 3h, centrifuging to remove the lower white solid, performing ultrasonic dispersion on the white solid in water again, and performing centrifugal washing. Repeating the centrifugal washing operation for 3-4 times to wash out excessive polydiallyl dimethyl ammonium chloride, and then vacuum drying at 80 ℃ for 4 hours to obtain modified positively charged SiO 2 . From the transmission electron microscope FIGS. 2a and 2b, it can be seen that SiO before and after modification 2 The morphology of (C) is unchanged and the diameter is about 280nm. Obtained by Zeta potential detection, siO of-23.8 mV 2 The potential after modification becomes +30.1mV, which proves that SiO 2 The surface modification was successful.
Example 2
The prepared 30mg GDY is fully ground, and then is subjected to 200W ultrasonic treatment for 3 hours to obtain a small-sized lamellar GDY, and the lamellar GDY is dispersed in 10mL of water for later use. 120mg of modified positively charged SiO prepared according to the scheme of example 1 2 Ball sonicated for 30min was dispersed in 30mL water, and all GDY aqueous solution was added and stirred for 3 hours while stirring was maintained. Centrifuging at 10000r/min for 10min to obtain black solid, and vacuum drying at 70deg.C to obtain black solid SiO 2 @ GDY. SiO is made of 2 After being fully ground, GDY mg of dicyandiamide and 800mg of dicyandiamide are put into a tube furnace, nitrogen is introduced, the heating rate is 5 ℃/min, the temperature is raised to 800 ℃ and maintained for 1h. After natural cooling, 100mg of pyrolyzed product (SiO 2 @ N-GDY) was added to 45mL of 10% HF solutionAfter etching for 8 hours at room temperature, filtering the etched mixture to obtain solid, centrifugally washing the solid with deionized water to be neutral, and vacuum drying the solid at 70 ℃ to obtain the hollow sphere electrocatalyst (N-GDYHS) containing sp-nitrogen doped graphite alkyne.
FIGS. 3a and 3b show the GDY fragment before and after ultrasonic grinding by physical means, and it has been found that the large GDY size is successfully reduced in size; fig. 3c shows that GDY and SiO2 spheres are adsorbed together after being mixed and stirred due to the attraction of positive and negative charges. FIG. 4a shows that graphite alkyne is still firmly encapsulated in SiO after pyrolysis 2 The balls, while pyrolysis treatment increases the graphitization degree of the carbon material, thereby enhancing conductivity. As can be seen from FIG. 4b, siO is added 2 After ball etching, siO 2 N-GDY changes from solid structure to hollow sphere structure (N-GDYHS), and N-GDYHS substantially retains SiO 2 The original spherical shape and diameter of the ball are that the thickness of the hollow ball is about 5.8 nm. Fig. 5 is a high resolution XPS spectrum of N1s, in which the bonding mode of nitrogen element is divided into four, namely graphite nitrogen (400.9 eV), amino nitrogen (399.4 eV), pyridine nitrogen (398.4 eV) and sp-N (397.6 eV), which illustrates that nitrogen element is successfully doped into graphite alkyne hollow sphere shell, and demonstrates that partial nitrogen element and carbon element exist in sp hybridized form bonding.
Example 3
Preparation of surface-modified SiO by the method in example 1 2 Wherein 50mg of SiO is taken 2 And 0.1g of polydiallyl dimethyl ammonium chloride.
The prepared 50mg GDY was sufficiently ground and sonicated at 200W for 1.5h to obtain a small-sized lamellar GDY which was dispersed in 10mL of water for further use. 50mg of modified positively charged SiO prepared according to the scheme of example 1 are reacted 2 Ball sonicated for 30min was dispersed in 30mL water, and all GDY aqueous solution was added and stirred for 3 hours while stirring was maintained. Centrifuging at 10000r/min for 10min to obtain black solid, and vacuum drying at 80deg.C to obtain black solid SiO 2 @ GDY. SiO is made of 2 After being fully ground, the @ GDY mg and 1000mg melamine are put into a tube furnace, nitrogen is introduced, the heating rate is 10 ℃/min, the temperature is raised to 700 ℃ and maintained for 1h. Naturally cooling, collecting 100mg of heatThe product after decomposition (SiO 2 @ N-GDY) was added to 45mL of a 12% HF solution, etched at room temperature for 6h, the etched mixture was filtered to give a solid, which was washed to neutrality by centrifugation with deionized water, and dried in vacuo at 70deg.C to give an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst (N-GDYHS).
Example 4
The prepared 50mg GDY was sufficiently ground and sonicated at 100W for 3 hours to obtain a small-sized lamellar GDY which was dispersed in 10mL of water for further use. 120mg of modified positively charged SiO prepared according to the scheme of example 1 2 Ball sonicated for 30min was dispersed in 30mL water, and all GDY aqueous solution was added and stirred for 3 hours while stirring was maintained. Centrifuging at 10000r/min for 10min to obtain black solid, and vacuum drying at 80deg.C to obtain black solid SiO 2 @ GDY. SiO is made of 2 After being fully ground, GDY mg of biuret and 500mg of biuret are put into a tube furnace, nitrogen is introduced, the heating rate is 5 ℃/min, the temperature is raised to 900 ℃ and maintained for 1.5 hours. After natural cooling, 100mg of pyrolyzed product (SiO 2 @ N-GDY) was added to 45mL of a 5% HF solution, etched at room temperature for 12h, the etched mixture was filtered to give a solid, which was washed to neutrality by centrifugation with deionized water, and dried in vacuo at 70deg.C to give an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst (N-GDYHS).
Comparative example 1
The prepared 30mg GDY was directly dispersed in 10mL of water for further use. 120mg of modified positively charged SiO prepared according to the scheme of example 1 2 Ball sonicated for 30min was dispersed in 30mL water, and all GDY aqueous solution was added and stirred for 3 hours while stirring was maintained. Centrifuging at 10000r/min for 10min to obtain black solid, and vacuum drying at 70deg.C to obtain black solid SiO 2 @ GDY, siO 2 After being fully ground, GDY mg of dicyandiamide and 800mg of dicyandiamide are put into a tube furnace, nitrogen is introduced, the heating rate is 5 ℃/min, the temperature is raised to 800 ℃ and maintained for 1h. After natural cooling, 100mg of pyrolyzed product (SiO 2 @ N-GDY) was added to 45mL of a 10% HF solution, etched at room temperature for 8h, the etched mixture was filtered to give a solid and washed with deionized water centrifugally to neutrality, and at 70 ℃Vacuum drying to obtain the hollow sphere electrocatalyst (N-GDYHS) containing sp-nitrogen doped graphite alkyne.
As can be seen from the transmission electron microscope FIG. 4 of the catalyst prepared in comparative example 2 and the transmission electron microscope FIG. 6 of the catalyst prepared in comparative example 1, the large-sized GDY could not be uniformly coated on SiO without subjecting the prepared GDY to the downsizing treatment 2 The surface of the sphere eventually cannot obtain a graphite alkyne hollow sphere structure with uniform and stable thickness, which indicates that the miniaturization treatment of GDY is important for forming N-GDYHS. The catalyst prepared in comparative example 1 does not have a graphite alkyne hollow sphere structure with uniform and stable thickness, and can not maximally improve the mass transfer performance, thereby influencing the ORR catalytic performance. This is evident from the electrochemical test data in test examples 1 and 2, and the measurement result of example 2 is superior to that of comparative example 1.
Comparative example 2
Comparative example 2 was black solid SiO prepared in example 2 2 GDY100 mg is placed in a tube furnace, nitrogen is introduced, the heating rate is 5 ℃/min, the temperature is raised to 800 ℃ and maintained for 1h. After natural cooling, 100mg of the pyrolysed product was added to 45ml of 10% hf solution, after etching for 8h, the etched mixture was filtered to give a solid, which was washed to neutrality by centrifugation with deionized water and dried under vacuum at 70 ℃, as can be seen from XPS total spectrum analysis of example 2 and comparative example 2 (fig. 7), the product of comparative example 2 was found to be free of nitrogen, except for graphite alkyne nanospheres (GDYHS). In contrast to example 2, the catalyst prepared in comparative example 2 was not sp-N doped, whereas nitrogen doping was critical for the construction of the active sites. This is evident from the electrochemical test data in test examples 1 and 2, and the measurement result of example 2 is superior to that of comparative example 2.
Comparative example 3
100mg of the miniaturized GDY solid in example 2 and 800mg of dicyandiamide are fully ground, then the mixture is put into a tube furnace, nitrogen is introduced, the heating rate is 5 ℃/min, the temperature is raised to 800 ℃ and the mixture is kept for 1h. After natural cooling, a nitrogen doped graphite alkyne catalyst (N-GDY) can be obtained.
Example 2 differs from comparative example 3 in the control of the morphology of the hollow spheres, p-GDYAnd N-GDYHS was subjected to a nitrogen desorption test. As can be seen from the adsorption/desorption isotherm of N-GDYHS (FIG. 8), a rapid rise phenomenon occurs in the low pressure zone, indicating the presence of micropores, a distinct hysteresis loop occurs in the middle pressure zone, indicating the presence of mesopores, and the specific surface area of N-GDYHS is 382.3m as calculated from the adsorption/desorption isotherm of nitrogen 2 g -1 N-GDY has a specific surface area of 85m 2 g -1 The two-dimensional GDY is converted into the hollow sphere shape, so that the specific surface area of the hollow sphere shape can be effectively increased, the mass transfer performance in the ORR process can be accelerated, and the catalytic activity is improved.
Test example 1
5mg of the catalyst obtained in example 2, comparative example 1, comparative example 2, comparative example 3 and commercial 20wt% Pt/C catalyst were dispersed in a mixture of 50. Mu.L of Nafion solution (mass concentration: 5%), 600. Mu.L of ethanol and 350. Mu.L of deionized water, and sonicated for 30min to give a dispersion of 5mg/mL. Taking 10 mu L of the dispersion liquid to be coated on the surface of a glassy carbon electrode, naturally airing to obtain a film electrode as a working electrode; the platinum electrode is used as a counter electrode, the Ag/AgCl electrode is used as a reference electrode, and the electrolyte is O 2 Saturated KOH (0.1 mol/L) solution.
Oxygen reduction electrocatalytic performance testing was performed at the CHI660E electrochemical workstation with specific results shown in fig. 9. The half-wave potential, starting potential of 0.875V and 1.012V, respectively, of the catalyst prepared in example 2 was greater than the Pt/C and the catalysts of comparative examples 1-3, indicating that the N-GDYHS catalyst prepared in example 2 had excellent ORR performance under alkaline conditions.
Test example 2
5mg of the catalyst obtained in example 2, comparative example 1, comparative example 2, comparative example 3 and commercial 20wt% Pt/C catalyst were dispersed in a mixture of 50. Mu.L of Nafion solution (mass concentration: 5%), 600. Mu.L of ethanol and 350. Mu.L of deionized water, and sonicated for 30min to give a dispersion of 5mg/mL. Taking 10 mu L of the dispersion liquid to be coated on the surface of a glassy carbon electrode, naturally airing to obtain a film electrode as a working electrode; the platinum electrode is used as a counter electrode, the Ag/AgCl electrode is used as a reference electrode, and the electrolyte is O 2 Saturated H 2 SO 4 (0.5 mol/L) solution.
Oxygen reduction electrocatalytic performance testing was performed at the CHI660E electrochemical workstation with specific results shown in fig. 10. Example 2 preparation of catalyst N-GDYHS half-wave potential, starting potential 0.764V and 0.91V, respectively, catalysts substantially similar to Pt/C but much greater than those prepared in comparative examples 1-3. The N-GDYHS catalyst prepared in example 2 was shown to have better ORR performance under acidic conditions.
The porous structure and abundant active sites of the catalyst prepared by the invention are more in general, the more the porous structure is, the more the specific surface area is, the more the active sites are exposed to electrolyte, the better the electrocatalytic performance is, which can be reflected by the electrochemical performance test results of the test examples 1-2, and the electrochemical test results of LSV under the acidic condition and the alkaline condition show that the N-GDYHS prepared by the invention has excellent ORR catalytic performance, can be compared with commercial 20wt% Pt/C catalyst, and has lower cost.
Test example 3
5mg of example 2, commercially available 20wt% Pt/C catalyst was dispersed in a mixture of 50. Mu.L of Nafion solution (5% by mass), 600. Mu.L of ethanol and 350. Mu.L of deionized water, and sonicated for 30min to give a 5mg/mL dispersion. Taking 10 mu L of the dispersion liquid to be coated on the surface of a glassy carbon electrode, naturally airing to obtain a film electrode as a working electrode; the platinum electrode is used as a counter electrode, the Ag/AgCl electrode is used as a reference electrode, and the electrolyte is O 2 Saturated H 2 SO 4 (0.5 mol/L) solution and KOH (0.1 mol/L) solution.
Long-term stability testing was performed at the CHI660E electrochemical workstation by fixed potentiometric amperometry (CA), with specific results shown in fig. 11. The CA curve of N-GDYHS shows little decay after stability testing up to 20000s compared to commercial Pt/C catalysts, whether in acidic or basic environments. And as can be seen from TEM (figure 12), the morphology of the N-GDYHS hollow sphere can be well maintained after long-term stability test, which shows that the result has higher stability.

Claims (10)

1. Hollow graphite alkyne containing sp-nitrogen dopingThe spherical electrocatalyst is characterized in that the hollow spherical electrocatalyst containing sp-nitrogen doped graphite alkyne is SiO modified by polydiallyl dimethyl ammonium chloride 2 Ball as hard template, in SiO 2 Uniformly wrapping nitrogen-doped graphite alkyne on the surface of the ball, and finally removing SiO 2 Ball formation;
the preparation method of the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne comprises the following steps:
（1）SiO 2 modification of the ball: siO is made of 2 Adding the balls into NaCl solution for ultrasonic dispersion, then adding polydiallyl dimethyl ammonium chloride for stirring, centrifugally washing and vacuum drying to obtain modified positively charged SiO 2 A ball;
(2) Miniaturization of GDY: sufficiently grinding graphite alkyne, dispersing in water, and carrying out ultrasonic treatment to obtain a lamellar GDY solution with small size;
（3）SiO 2 preparation of @ N-GDY: the modified positively charged SiO obtained in the step (1) is subjected to 2 Dispersing the spheres in water, mixing the dispersion with the small-sized lamellar GDY solution obtained in the step (2), stirring, centrifuging and drying to obtain solid SiO 2 GDY solid SiO 2 Grinding @ GDY and N-containing organic micromolecules, and carbonizing at high temperature in inert gas to obtain SiO 2 @N-GDY；
(4) Preparation of sp-N doped graphite alkyne nano hollow sphere electrocatalyst: siO obtained in the step (3) is reacted with 2 Dispersing @ N-GDY in an HF solution, stirring for etching, centrifugally washing the etched mixture to be neutral by using deionized water, and vacuum drying to obtain the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne.
2. The hollow sphere electrocatalyst comprising sp-nitrogen doped graphite alkyne of claim 1, wherein the hollow sphere electrocatalyst comprising sp-nitrogen doped graphite alkyne has an inner diameter and SiO used 2 The spheres have the same diameter and the hollow spheres have a thickness of 5-11nm.
3. A method for preparing the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne as claimed in claim 1, comprising the steps of:
（1）SiO 2 modification of the ball: siO is made of 2 Adding the balls into NaCl solution for ultrasonic dispersion, then adding polydiallyl dimethyl ammonium chloride for stirring, centrifugally washing and vacuum drying to obtain modified positively charged SiO 2 A ball;
(2) Miniaturization of GDY: sufficiently grinding graphite alkyne, dispersing in water, and carrying out ultrasonic treatment to obtain a lamellar GDY solution with small size;
（3）SiO 2 preparation of @ N-GDY: the modified positively charged SiO obtained in the step (1) is subjected to 2 Dispersing the spheres in water, mixing the dispersion with the small-sized lamellar GDY solution obtained in the step (2), stirring, centrifuging and drying to obtain solid SiO 2 GDY solid SiO 2 Grinding @ GDY and N-containing organic micromolecules, and carbonizing at high temperature in inert gas to obtain SiO 2 @N-GDY；
(4) Preparation of sp-N doped graphite alkyne nano hollow sphere electrocatalyst: siO obtained in the step (3) is reacted with 2 Dispersing @ N-GDY in an HF solution, stirring for etching, centrifugally washing the etched mixture to be neutral by using deionized water, and vacuum drying to obtain the hollow sphere electrocatalyst containing sp-nitrogen doped graphite alkyne.
4. The method according to claim 3, wherein SiO in the step (1) 2 The mass ratio of the modified poly (diallyl) dimethyl ammonium chloride to the poly (diallyl) dimethyl ammonium chloride is 1-2:4.
5. The method according to claim 3, wherein the ultrasonic time in the step (2) is 1.5-3h, the ultrasonic power is 100-200W, and the concentration of the GDY liquid is 1-5mg/mL.
6. The process according to claim 3, wherein the modified positively charged SiO in step (3) 2 The mass ratio of the ball to the graphite alkyne is 1:0.25-1.
7. The method according to claim 3, wherein the small N-containing organic molecules in the step (3) are melamine, biuret or dicyandiamide, siO 2 The mass ratio of the @ GDY to the N-containing small organic molecules is 1:5-10.
8. The method according to claim 3, wherein the inert gas in the step (3) is nitrogen or argon, the heating rate of the high-temperature carbonization treatment is 5-10 ℃/min, the carbonization temperature is 700-900 ℃, and the carbonization time is 1-1.5h.
9. The method according to claim 3, wherein the volume concentration of the HF solution in the step (4) is 5-15%, and the etching time is 6-12 hours.
10. Use of an sp-nitrogen doped graphite alkyne-containing hollow sphere electrocatalyst according to claim 1 in a fuel cell cathode oxygen reduction reaction.
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